Semiconductor sheets and methods of fabricating the same

Abstract

A method of fabricating a sheet of semiconductor material is provided. The method includes forming a first layer of silicon powder that has a lower surface and an opposite upper surface. The method also includes depositing a second layer of silicon powder across the upper surface of the first layer, wherein the second layer of silicon powder has a lower surface and an opposite upper surface and has a lower melting point than the first layer of silicon powder. The method also includes heating at least one of the first and second layers of silicon powder to initiate a controlled melt of at least one of the first and second layers of silicon powder, and cooling at least one of the first and second layers of silicon powder to initiate crystallization of at least one of the first and second layers of silicon powder.

1 . A method of fabricating a sheet of semiconductor material, said method comprising:
 forming a first layer of silicon powder that has a lower surface and an opposite upper surface;   depositing a second layer of silicon powder across the upper surface of the first layer, wherein the second layer of silicon powder has a lower surface and an opposite upper surface and has a lower melting point than the first layer of silicon powder;   heating at least one of the first and second layers of silicon powder to initiate a controlled melt of at least one of the first and second layers of silicon powder; and   cooling at least one of the first and second layers of silicon powder to initiate crystallization of at least one of the first and second layers of silicon powder.   
     
     
         2 . A method according to  claim 1  wherein depositing a second layer of silicon powder further comprises adding an impurity to the second layer of silicon powder to facilitate reducing the melting point of the second layer of silicon powder as compared to the first layer of silicon powder. 
     
     
         3 . A method according to  claim 2  wherein adding an impurity to the second layer of silicon powder comprises adding at least one of iron and copper to the silicon powder. 
     
     
         4 . A method according to  claim 1  wherein heating at least one of the first and second layers comprises applying heat to the upper surface of the second layer of silicon powder to cause the second layer of silicon powder to melt. 
     
     
         5 . A method according to  claim 4  wherein heating at least one of the first and second layers further comprises applying heat to the lower surface of the first layer of silicon powder such that a temperature at the lower surface of the first layer is lower than a temperature at the upper surface of the second layer. 
     
     
         6 . A method according to  claim 1  further comprising determining when the second layer of silicon powder has liquified. 
     
     
         7 . A method according to  claim 6  further comprising discontinuing heating of the upper surface of the second layer of silicon powder after determining that the second layer of silicon powder has liquified. 
     
     
         8 . A method according to  claim 6  further comprising increasing the magnitude of heat applied to the lower surface of the first layer of silicon powder after determining that the second layer of silicon powder has liquified. 
     
     
         9 . A method according to  claim 6  wherein cooling at least one of the first and second layers comprises extracting heat from the upper surface of the second layer of silicon powder to initiate crystallization of at least a portion of the second layer of silicon powder after determining that the second layer of silicon powder has melted. 
     
     
         10 . A method according to  claim 9  wherein extracting heat comprises applying a heat extractor to at least one of the upper surface of the second layer and the lower surface of the first layer. 
     
     
         11 . A method of fabricating a semiconductor wafer, said method comprising:
 forming a first layer of silicon powder that has a lower surface and an opposite upper surface;   depositing a second layer of silicon powder across the upper surface of the first layer, wherein the second layer of silicon powder has a lower surface and an opposite upper surface and has a lower melting point than the first layer of silicon powder;   heating at least one of the first and second layers of silicon powder to initiate a controlled melt of one of the first and second layers of silicon powder;   cooling at least one of the first and second layers of silicon powder to initiate crystallization of at least one of the first and second layers of silicon powder to form a silicon sheet; and   cutting the silicon sheet to form at least one semiconductor wafer, wherein the at least one semiconductor wafer is sized to facilitate use in a predetermined application.   
     
     
         12 . A method according to  claim 11  wherein depositing a second layer of silicon powder further comprises adding an impurity to the second layer of silicon powder to facilitate reducing the melting point of the second layer of silicon powder as compared to the first layer of silicon powder. 
     
     
         13 . A method according to  claim 12  wherein adding an impurity to the second layer of silicon powder comprises adding at least one of iron and copper to the silicon powder. 
     
     
         14 . A method according to  claim 11  wherein heating at least one of the first and second layers comprises applying heat to the upper surface of the second layer of silicon powder to cause the second layer of silicon powder to melt. 
     
     
         15 . A method according to  claim 14  wherein heating at least one of the first and second layers further comprises heating the upper surface of the second layer to a higher temperature than a temperature at the lower surface of the first layer of silicon powder. 
     
     
         16 . A method according to  claim 11  further comprising discontinuing heating of the upper surface of the second layer of silicon powder after the second layer of silicon powder has liquified. 
     
     
         17 . A method according to  claim 15  further comprising increasing a magnitude of heat applied to the lower surface of the first layer of silicon powder after the second layer of silicon powder has liquified. 
     
     
         18 . A method according to  claim 11  wherein cooling at least one of the first and second layers comprises extracting heat from the upper surface of the second layer of silicon powder to initiate crystallization of at least a portion of the second layer of silicon powder. 
     
     
         19 . A sheet of semiconductor material having a lower surface and an opposite upper surface, said sheet of semiconductor material having a higher concentration of metal impurities at the lower surface than any other portion of said sheet, said sheet of semiconductor material fabricated by a process comprising:
 forming a first layer of silicon feedstock that has a lower surface and an opposite upper surface;   depositing a second layer of silicon feedstock across the upper surface of said first layer, wherein said second layer of silicon feedstock comprises a silicon powder and a metal impurity and has a lower melting point than said first layer of silicon feedstock;   heating at least one of said first and second layers of silicon feedstock to initiate a controlled melt of at least one of said first and second layers of silicon feedstock; and   cooling at least one of said first and second layers of silicon feedstock to initiate crystallization of at least one of said first and second layers of silicon feedstock, wherein the heating and the cooling facilitates segregation of said metal impurity towards the lower surface of said first layer of silicon feedstock.